Justification:
This species is listed as Least Concern in view of its wide distribution, large population, and because it is not declining at anything close to the rate required to qualify for listing in a threatened category.

The bighorn sheep ranges widely in western Canada, western United States, and northern Mexico.

In Canada, the bighorn sheep (O. c. canadensis) is distributed throughout the Rocky Mountains in Alberta and British Columbia, south from the Peace River to the Canada-USA border. Two small populations also have been introduced to central British Columbia outside their normal distribution. Populations of a second subspecies, California bighorn sheep (O. c. californiana), are scattered through central British Columbia from north of Anahim lake, south along sections of the Chilcotin, Chilco and other western tributaries of the Fraser river south of William’s Lake and west to just north of Lillooet, and also south from around Kamloops along both sides of the Okanagan valley to the border with Washington State (USA) and as far west as Granby, British Columbia. Populations around Kamloops and Granby have been introduced, mostly into historically occupied habitat.

In the United States, the bighorn sheep is widely distributed from Montana and Idaho south through Wyoming and northern Utah, to Colorado and New Mexico. These bighorn herds comprise most of the traditional O. c. canadensis for which Thorne et al. (1985) estimated a population of greater than 19,000. To the south, desert bighorn (traditionally O. c. nelsoni, O. c. cremnobates, and O. c. mexicana) inhabit southern portions of California, Nevada, Utah and New Mexico, much of Arizona, and west Texas. Weaver (1985) estimated 16,000 desert bighorn in this area. However, there are few bighorn and few herds (mostly transplants to reintroduce bighorns in areas where they were extirpated) within the Chihuahuan desert of New Mexico and west Texas. To the west, bighorn occur in scattered populations in the Columbia plateau and Great Basin ranges of Washington, Oregon, southwest Idaho, and northern Nevada. These herds comprise most of the traditional O. c. californiana, for which Thorne et al. (1985) estimated greater than 2,800 animals. East of the Rocky Mountains, bighorn exist in scattered herds in badlands and river-breaks in eastern Montana, North and South Dakota, northeast Wyoming, Nebraska, and outside of historic range in southeast Colorado.

In Mexico, the bighorn sheep was originally distributed in the northern states of Nuevo Leon, Coahila, Chihuahua, Sonora, Baja California and Baja California Sur. Desert bighorn in Mexico is now restricted to three states: Mexican bighorn (O. c. mexicana) in northwestern Sonora and on Tiburon island in the Sea of Cortez; Peninsular bighorn (O. c. cremnobates) in the northern two thirds of Baja California; and Weems’ bighorn (O. c. weemsi) in the southern third of Baja California Sur.

The total population of all bighorn sheep in Canada is estimated to be ca. 15,500 to 15,700 individuals. Of this total, ca. 11,500 to 11,700 are estimated to be Rocky Mountain bighorns [Alberta 10,300 (K. Smith, in litt., 1994), and British Columbia 1,500 to 1,700 (Hebert et al., 1985)], and ca. 4,000 California bighorn whose individual populations range in size from 15 to 2,400 animals. Most populations of both subspecies are either increasing or stable.

In 1990, there were estimated to be greater than 42,700 bighorn sheep in over 340 recognized herds, in 14 of the states in the United States. However, 64% of the herds recently had less than 100 animals (Thorne et al., 1985; U. S. Bureau of Land Management, n.d.), but most of these populations have since increased.

Only rough population estimates are available for Mexico. Previous estimates of 4,500 in all of Baja California, and perhaps 1,000 on ten separate ranges in Sonora (Sandoval, 1985) were inaccurate. A helicopter survey of the northern two thirds of Baja California in April 1992 by the Bighorn Institute, revealed there were probably greater than 2,500 wild sheep in the entire peninsula (J. Deforge pers. comm., 1992). Personnel from the Arizona Game and Fish Department and the Centro Ecologico de Sonora, conducted a helicopter survey of the principal mountain ranges of Sonora, Mexico in November 1992. Based on this survey, during which 528 sheep were classified by age and sex, R.M. Lee (pers. comm., 1992) estimated ca. 2,000 wild sheep for Sonora. The total estimate of all desert bighorn sheep in Mexico in 1992 was therefore ca. 4,500 animals.

These animals are sexually segregated outside the rut. Group sizes usually range from 5 to 50 for males and from 5 to 100 for ‘nursery’ groups of females, lambs and young males.

They mostly eat grass, but they also consume forbs and browse – diet varies widely over the large geographical range of the species. Females gestate for 175 days, and give birth to a single offspring per pregnancy. Females can first conceive at 18 months of age and males are rarely successful at obtaining paternities before about 3 years of age. Very few females live more than 15 years and very few males survive past 12 years.

Epizootics have occurred periodically, especially in Rocky Mountain bighorn, and together with over-harvesting and competition from livestock at the end of the 19th century and beginning of the 20th, reduced numbers significantly. Most populations recovered with the aid of wildlife management and conservation efforts, but pneumonia and mange epizootics still occur today, particularly in populations that come into contact with domestic sheep and goats. Poaching of large trophy males is a problem in many areas, including within national parks.

In the US, small (< 100) numbers in many herds, and diseases from domestic sheep are major threats, while in Mexico the threats are poaching, competition from domestic livestock, and habitat degradation (Sandoval, 1985).

In Canada, more than 4,500 Rocky Mountain bighorns are fully protected within five National Parks (Banff, Jasper, Kootenay, Waterton, Yoho). An even larger number receive some level of protection in provincial parks and other protected areas in Alberta and British Columbia. Animals in protected areas are often especially vulnerable to poaching because they are habituated to humans and are also readily accessible. Outside national parks, both subspecies of bighorn sheep are covered by provincial or state wildlife acts, and many populations can be hunted under license. Harvesting both adult males and adult females may be permitted in some populations. Hunting quotas are determined each year, and in general regulations are strictly enforced. Management consists of regulating annual harvests, habitat improvement, annual censuses, translocation of animals, and promoting research. Between 200 to 250 male and 150 to 200 female Rocky Mountain bighorns are harvested annually in Alberta. In British Columbia, where only males are hunted: 60 to 65 Rocky Mountain and 40 to 45 California bighorns are shot each year, mainly by resident hunters (Hebert et al., 1985). In much of Canada, male harvest is limited only by the availability of adult males that have reached a minimum curl size, possibly leading to artificial selection against large-horned rams (Coltman et al., 2003).

In the US, Bighorn sheep occur in the following 30 National Parks, Monuments, Recreation Areas and Wildlife Refuges: Arizona: Grand Canyon NP; Cabeza Prieta, Havasu, and Kofa WRs; Glen Canyon, and Lake Mead NRAs; Organ Pipe Cactus NM; California: Sequoia- Kings Canyon NP; Death Valley, and Joshua Tree NMs; Colorado: Mesa Verde, and Rocky Mountain NPs; Colorado, and Dinosaur NMs; Montana: Glacier, and Yellowstone NPs; Bison Range, and C.M. Russell NWRs; Bighorn Canyon NRA; Nevada: Desert NWR; Death Valley NM; Lake Mead NRA; New Mexico: San Andres NWR; North Dakota: T. Roosevelt NP; Oregon: Hart Mountain NWR; South Dakota: Badlands NP; Utah: Arches, Canyonlands, Capitol Reef, and Zion NPs; Dinosaur NM; Flaming Gorge, and Glen Canyon NRAs; Wyoming: Grand Teton, and Yellowstone NPs; Bighorn Canyon NRA. It also occurs in the large Anza-Borrego State Park (California). Most of these protected areas are in the Mojave and Sonoran deserts, and on the Colorado plateau. Numerous other federal lands administered by the Forest Service and Bureau of Land Management also contain bighorn. Fourteen state wildlife agencies have transplanted sheep onto more than 200 historic ranges. This has accounted for much of the recovery of bighorn sheep from historic low numbers in the 1960s. However, numerous other transplants have failed (Bailey, 1990), presumably for lack of careful evaluation of habitat conditions at potential transplant sites or because of disease transmitted by livestock. Animals in about half the herds are hunted, and all states with bighorn sheep have at least one hunted population. Usually, only adult males are taken as hunting trophies. The number of sheep permitted to be taken each year is conservative and is regulated by each state. All states require that legally taken trophy heads be marked for permanent identification. This practice allows easy identification of illegally taken animals and thus discourages poaching.

Improvement of habitat for bighorn sheep has been frequent, especially on federal multiple-use lands. Projects have been funded with combinations of federal, state, and private moneys. Natural water sources have been improved and artificial water sources created, especially in the Mojave and Sonoran deserts of the Southwest. Further north, dense forest or shrub vegetation has been cleared, often by controlled burning, to provide open areas with forage for bighorn sheep. Some populations of bighorn are routinely baited and treated with drugs to control parasites including lungworm (Protostrongylus sp.). Such treatments concentrate sheep and may jeopardize wildness. Management and research biologists exchange information on bighorn sheep in annual meetings of the Desert Bighorn Council and biennial meetings of the Northern Wild Sheep and Goat Council. Proceedings of these meetings are published. Three private organizations, the Foundation for North American Wild Sheep, the Rocky Mountain Bighorn Society and the Society for the Conservation of Bighorn Sheep, raise funds for research and management. At least 10 states auction and/or raffle one or two special bighorn hunting licenses to raise funds for these purposes. Its status within the United States is Not Threatened (but see below).

The status of most traditional subspecies and major ecotypes of bighorn sheep is satisfactory because they exist on 30 biological reserves and on many other protected areas. However, their status is not fully secure because at least 64% of the herds contain about 100 animals. Berger (1990) reviewed the history of some small bighorn populations and concluded that those numbering less than 50 animals usually became extirpated, but Wehausen (1999) provides an alternative interpretation and viewpoint. Further, the ecotypes of bighorn in the Chihuahuan desert and in shortgrass-badlands and riverbreak environments are not secure because there are few reserves or other protected lands within these two regions, and very few of these lands contain wild sheep.

Conservation measures proposed for the United States: 1) Additional research on bighorn diseases, particularly in relation to domestic livestock, and on developing efficient methods for habitat management is desirable. 2) State and federal agencies should develop coordinated plans to enhance the long-term security of the numerous bighorn herds with less than 100 sheep. Strategies should include increasing herd size, expanding habitat and increasing herd mobility, and enhancing habitat quality and habitat protection in corridors between small herds (Bailey 1992). 3) Land management agencies, especially the U.S. Forest Service and Bureau of Land Management, should formally recognize bighorn ranges in their management plans, including corridors for movement within and between herds. 4) Until disease relations are clearer, bighorn should be protected from contact with domestic sheep and domestic goatswhenever possible. 5) Greater recognition of the values and importance of ecotypic variation in bighorn sheep is needed. Federal agencies and state wildlife departments should seek a consensus on classifying the major ecotypes. Each state should furthermore classify its bighorn according to state ecotypes. Conservation of major ecotypes should proceed under the federal Endangered Species Act. Each state should be responsible for conserving another level of ecotypic diversity of bighorn sheep within its boundaries. 6) Increase the number of bighorn sheep in federally protected habitats in the Chihuahuan Desert and in the shortgrass-badlands and river breaks ecosystems. In the Chihuahuan Desert, options include: a) expanding protection of habitat and sheep from the San Andres National Wildlife Refuge to a greater portion of the White Sands Missile Range; b) formally recognizing and enhancing protection of the Big Hatchet Game Range, now on Bureau of Land Management land; c) establishing viable bighorn populations in Guadalupe Mountains and Big Bend National Parks; and d) establishing bighorn in a new biological reserve, probably in west Texas. 7) In the shortgrass-badlands and river breaks ecosystems, management options include: a) expanding bighorn populations and distributions in the Charles M. Russell National Wildlife Refuge, the Bighorn National Recreation Area, and in Theodore Roosevelt and Badlands National Parks; and b) establishing bighorn populations in new biological reserves in eastern Wyoming or western Nebraska.

The species in Mexico is listed in Appendix II of CITES. Mexican bighorn occur in only two protected areas in Mexico, one of which (Isla Tiburon Wildlife Reserve (in the Sea of Cortez)) holds an introduced population. Peninsular bighorn is in only one protected area, Sierra de San Pedro Martir National Park, but Weem’s bighorn occurs in none. A small group (25 in 1992) of desert bighorn (O. c. nehoni) is held in captivity at Hermosillo. The high price ($30,000 to over $l00,000) that some hunters are willing to pay to hunt wild sheep has recently motivated private and communal landowners in Sonora and Baja California to begin desert sheep monitoring and management programs. In 1994, ranchers in Sonora started a captive breeding program by capturing 40 sheep and placing them in breeding enclosures. Six hunting permits were issued to private landowners for free-ranging bighorns in 1995, and each sold for $40,000. A private conservation organization has initiated a transplant of Weem’s bighorn from southern Baja California to Carmen Island. The excess sheep produced on this island, once the transplanted population increases to a viable size, will be used to re-establish extinct populations on the mainland. The participation of private landowners in wild sheep management programs in Mexico is a positive initiative. Private landowners have the funds to provide for monitoring wild sheep populations and to prevent further poaching.

Conservation measures proposed for Mexico: At least five areas must be addressed for conservation of desert bighorn in Mexico (Sandoval, 1985): a) Effective law enforcement is a major problem facing the conservation of bighorn in Mexico. In large part, this is due to the very low financial support generally given to wildlife programmes. b) There is a general lack of technical expertise among wildlife personnel. c) A public education program, especially targeted towards the rural population, is necessary if conservation programmes are to be successful. d) Habitat management has generally been ignored, despite the fact that agricultural practices and forest use have had, and continue to have, significant negative effects on the bighorn. e) The further spread of exotic ungulates, such as Barbary sheep, in or adjacent to current and historic bighorn range should be curtailed. Proposals to deal with these include: 1) Increase the number of protected areas in Baja California and in Sonora on the mainland. Present protected areas are inadequate to protect sheep populations. Mexico’s burgeoning human population requires intensive exploitation of agricultural and natural resources, while coastal tourist development projects in Sonora and Baja California will have further deleterious impacts on wild sheep habitats. 2) Raise enforcement of anti-poaching efforts to adequate levels. This will require a well-equipped law enforcement division. 3) Develop a public conservation education programme, especially targeted towards the rural population. This could play an important role for future conservation of wild sheep and all other wildlife and natural resources. 4) Educate and employ a cadre of professional wildlife biologists.

In-Place Research, Monitoring and PlanningIn-Place Land/Water Protection and Management Conservation sites identified:Yes, over entire rangeIn-Place Species Management Harvest management plan:YesIn-Place Education Included in international legislation:Yes Subject to any international management/trade controls:Yes

Hogg, J. T., Forbes, S. H., Steele, B. M. and Luikart, G. 2006. Genetic rescue of an insular population of large mammals. Proceedings of the Royal Society of London B Biological Sciences 273: 1491-1499.